In electrical engineering, the term charging station denotes any stationary apparatus or electrical installation which serves to feed energy to mobile rechargeable battery-operated devices, machines or motor vehicles by simple positioning or plugging-in, without having to remove the energy storage element—for instance the traction battery of an electric automobile. Charging stations for electric automobiles are colloquially also referred to as “electricity charging stations” and can comprise a plurality of charging points, which are characterized as “charging columns” depending on the design.
Known systems here include in particular direct current (DC)-based rapid charging systems (high performance charging, HPC), such as the so-called combined charging system (CCS) widely used in Europe. In direct-current charging of the generic type, direct current is fed from the charging column directly into the vehicle and, for this purpose, is provided from the electricity grid by means of a powerful rectifier or at solar charging stations by means of large buffer rechargeable batteries. Situated in the vehicle there is a battery management system that communicates with the charging column in order to adapt the current intensity or to end the process when a capacity limit is reached.
According to the prior art, the power electronics required for this purpose are usually integrated in the charging column and have a loading capacity up to a power limit of 50 kW. Since the direct-current connections of the charging column are directly connected to corresponding connections of the traction battery, high charging currents can thus be transmitted with low losses, which enables short charging times.
However, modern electric high-performance vehicles and utility vehicles use voltages for their drive systems which sometimes are far above the output voltages of typical fast charging columns of often less than 400 V. In order nevertheless to be able to charge at existing fast charging columns, it is necessary to carry out a DC voltage conversion that raises the voltage of the charging column for example from 400 V to 800 V for the vehicle battery.
Said DC voltage conversion can be performed by a dedicated DC-DC converter, although this is expensive on account of the high power required, occupies a large structural space and significantly increases the vehicle weight, as a result of which the range is adversely affected.
US2004178756A, US2009230917A and US2013187446A, all of which are incorporated by reference herein, for instance, each disclose an electric vehicle battery safety system having a DC-DC converter. The respective system is configured to ascertain whether a limit value has been reached: a voltage limit is ascertained in the case of US2004178756A and US2009230917A, and a temperature limit in the case of US2013187446A.
US2017126165A, which is incorporated by reference herein, likewise relates to an electric vehicle battery safety system having a power converter. This system comprises a current and voltage sensor in order to ascertain whether a limit value has been reached and specific low-voltage-side switches are blocked.
U.S. Pat. No. 5,687,066A, which is incorporated by reference herein, discusses an electric vehicle battery safety system having a DC-DC converter, which system comprises a temperature sensor in order to ascertain whether a limit value has been reached.
Alternatively, the drive inverter of the vehicle can be used as a DC-DC converter. In this case, the conversion is effected via the phase inductance of the electric machine (from phase to star point). A major problem in the use of the drive inverter and the machine is the superimposed alternating current (ripple current) that arises on account of the often low machine phase inductance and the low possible switching rate of the slow insulated-gate bipolar transistors (IGBTs) used in vehicles. This current and voltage ripple in the case of the very high charging powers of present-day vehicles (100-500 kW, corresponding to the power supply of a village) generates strong electromagnetic interference in many sensitive electronic systems in the vehicle and causes increased energy losses accompanied by heating.